1. Field of the Invention
The invention relates to a magnetic flowmeter for measuring the flow of a flowing medium having a measuring tube, a unit for generating a magnetic field that generates a magnetic field at least partially permeating the measuring tube, two electrodes for detecting a measuring voltage induced in the flowing medium and a housing incorporating the measuring tube, preferably also the unit for generating a magnetic field and the electrodes, wherein the measuring tube has a cross section that changes over its length and preferably the cross section in the middle section of the measuring tube is less than at the beginning and end of the measuring tube, preferably the cross section of the measuring tube is rectangular in its middle section or square and wherein the housing preferably has a circular cross section.
2. Description of Related Art
Magnetic flowmeters have been known extensively from the prior art for decades; see, Technische Durchflussmessung” by Prof. Dr.-Ing. K. W. Bonfig, 3. Edition, Vulkan-Verlag Essen, 2002, pages 123 to 167 for a description.
The basic principle of a magnetic flowmeter for measuring the flow of a flowing medium goes back to Faraday, who, in the year 1832, suggested using the principle of electrodynamic induction for measuring the velocity of flow of a flowing medium. According to Faraday's law of induction, electrical field intensity is created perpendicular to the direction of flow and perpendicular to the magnetic field in a flowing medium that carries charge carriers along with it and flows through a magnetic field. Faraday's law of induction is used by magnetic flowmeters in that a magnetic field is created by a unit for generating a magnetic field, which normally has two magnetic coils supplied with current, and at least partially lead through a measuring tube, wherein the generated magnetic field has at least one component that runs perpendicular to the direction of flow. Within the magnetic field, each volume element of the flowing medium having the field intensity created in this volume element moving through the flowing medium and having a certain number of charge carriers contributes to a measuring voltage that can be detected via the electrodes.
As an example of the magnetic flowmeters that form the basis of this invention, German patent disclosures 197 08 857; 10 2004 063 617 and corresponding U.S. Pat. No. 7,261,001 B2; German patent disclosure 10 2008 057 756 and corresponding U.S. patent application 2010/132478 A1 are cited here. The content of these disclosures is hereby specifically incorporated by reference into the present application.